Jill Cakert, a dental hygienist and lifelong Eagles fan who lives in Ventnor, N.J., was familiar with Kelly's reputation when he was hired in January 2013. So she figured it couldn't hurt to send Kelly a model of her invention, the Signalfan. Cakert, a volunteer softball coach, originally created the Signalfan to make it easier to communicate with her players on the field. The device consists of several colored blades that can be rearranged in different combinations.

Shortly after sending Kelly one of her models, she got a note back from the coach along with a personal check for $25 (the Signalfan sells for $24.99 on its website): "It's been a big help!!" the coach wrote. "Great idea!!"

The device has been spotted on the Eagles' sideline this year:

Cakert is thrilled to see her team using the device, although she admits she has no idea how the Eagles are using it.

"I have no clue what they're using it for," she told the Philadelphia Inquirer. "They have so much going on on the sidelines, you see Chip Kelly with his tongue out talking, somebody doing hand signals. They could be using it as a decoy for all I know."

Kelly wouldn't reveal much either when asked about the Signalfan recently.

"It's just another way to communicate what we're doing on game days," he said.